Carrier-wave signaling system



Nov. 9 1926.

H. M. PRUDEN CARRIER WAVE SIGNALING SYSTEM Filed Oct. '7 1925 RBFlnven/or: H o/d/ lP/z/de/v by .A/fy

Patented Nov. v9, 1926.

UNITED STA HAROLD M. PBUDEN, OE WYOMING, NEW JERSEY, ASSIGNOR TO WESTERNELECTRIC COMPANY,'INCOBIPOBATED, OF NEW YORK, N. Y., A. CORPORATION OFNEW YORK.

CABRIEILWAVE SIGNALING SYSTEM.

Application med October 1, 1925. Serial No. 60,864.

. This invention relates to carrier wave signaling systems andparticularly to ringing circuits therefor.

An object of the invention is to simplify the transmission of ringingsignals in carrier telephone systems.

The invention is particularly, but not ex,-

1 with a ringing current, provided, of course, the side band produced bysuch modulation ,lies'within the transmission range of, the

terminal band filter.

This method of transmitting. ringing signals is facilitated in thepresent invention by the provision of a novel circuit for connecting avoice frequency composite ringer to the terminal of a carrier telephonechannel without unbalancing the associated .hy-

. brid circuit. The invention 'efiects a mate: rial saving' inapparatus, and possesses the further advantage that it may be reaapplied to existing carrier systems without otherwise changing thesystem.

The accompanying drawing is a diagrammatic illustration of one terminalof a multiplexv carrier wave telephone system embodying the invention.

The drawing'shows the necessary circuits which would enable one toconduct a complete two-way conversation from low fre-' quency line Lover to a distant station, and to transmit and receive ringing signalsover the multiplex line.

The low frequenc line L may be an ordinary subscribers te ephonecircuit. A radiating conductormay, of course, be employed in place ofthe line ML when it is desired to apply the invention to radio systems.

The low frequency line L is associated with the transmitting channel TCand the receiving channel RC of the carrier system through the usualhybrid coil H and associated balancing network N. Additionaltransmitting and receiving channels may also be provided, as indicated.The transmitting channel TC includes the modulator M, oscillator TO andband filter TBF. Receiving channel RC includes dethe multiplex line M1bell,

modulator and amplifier DA, oscillator R0 and band filter RBF.

The modulators associated with the various' transmitting channelsthroughout the sistem are of the balanced typedisclosed in t e U.S.,patent to Carson, No. 1,343,306,

issued June 15, 1920, designed to suppressthe unmodulated carrier fromtransmission. The various demodulators and amplifiers "may be of thewell known vacuum tube detector type shown in Fig. 49 ofan article.entitled Carrier current telephony and telegraphy by Messrs. Colpittsand Blackwell, ublished in the Transactions of the American Institute ofElectrical Engineers, V01. 40, 1921.

The carrier system outlined above is, as

stated, of the type in which the carrier wave of each channel is supressed from transmission when nosigna are being sent, and whensignalsare being transmitted modulation components of the modulated wave aresent .over the line, but no unmodulated components of the carrier waveare transmitted.

In order to reproduce the signals from.

modulated waves of this character, it is necessary that the carrier wavesupplied to the' demodulator at the receiver be of substantially thesame frequency as the carrier wave which was suppressed at thetransmitter. A system of this general character is described inconnection with Fig. 49 of the Colplitts and Blackwell article, supra".

T e various band filters associated with the terminal' transmitting andreceivin' channels are so designed that the wil transmit one of thesidebands, either t e upper or lower as desired, produced by modulation,inthe respective channels, and will suppress from transmission frequencieslying outside of such band. These filters may be designed in accordancewith the principles setforth in the U. S. patent to. Camp- No.1,227,113, issued May 22, 1917.

The hybrid coil H is of the well known balanced type including threewindings,'inductively related to each other. One wind-, ing may becalled a series winding andthe/ other two, line windings. Tappedofi froman intermediate point of each line. winding 1 is a bridge circuit, whichin the present case that, when the proper values of impedance areconnected across the several terminals, energy impressed upon the seriesWinding will not affect the bridge circuit and vice versa. For a furtherdescription of hybrid coils reference may be had to an article byMessrs. Gherardi and Jewett entitled Telephone repeaters published inthe Transactions of the American Institute of.

Electrical Engineers, Vol 38, N o. 11, October 1919 From the above, itwill be seen that voice currents originating in the low frequency line Lwill pass through the line windin s of the hybrid coil H into themodulator M 1n the transmitting channel TC. There is likewise fed intothe modulator the carrier current from the oscillator TO. Of thecomponents of modulation appearing in the output circuit of themodulator M, the band filter TBF suppresses all except one side' band,for example, the upper side band, which it transmits to the multiplexline ML. The waves so transmitted over the line ML are picked up byone'of the receiving band filters at the distant terminal andtransmitted to the appropriate receiving channel.

The waves incomin over the line LIL of the frequency assigne to channelRC pass through band filter RBF and are combined in the demodulator andamplifier DA with carrier waves from the source R0. The voice frequencycomponents of demodulation appearing in the output of receiving channelRC are inductively im ressed upon the line windings of the hybri coil Hand divide substantially equally between the low freqlpency line L andthe balancing networ N.

The hybrid coil H has four pairs of terminals, terminals 1 beingassociated with the series winding, terminals2 and 3 being associatedwith the line windings, and terminals comprising thebridge circuitterminals. The generator G provides a source of IOOO-cycle ringingcurrent periodically interrupted at the rate of 20 cycles per second forthe purpose of transmitting ringing signals as modulations of thecarrier frequency allotted to any channel of the multiplex system. Thismight be accomplished by connecting the generator G across the bridgecircuit terminals 4. but this procedure would materially increase thecost of the system and unnecessarily complicate the circuit for reasonshereinafter more fully 'described. If, on the other hand, the generatorG were connected directly to the line terminals 2, the resistance of thegenerator would unbalance the hybrid circuit during the ringingoperation and it would accordingly be necessary to substitute a networksimulating the impedance of the generator G for the line balancingnetwork N, which would also increase the cost of the system.

, The present invention provides a novel and inexpensiveswitchingarrangement for transmittin the ringing current from thegenerator diagonally through the hybrid coil H to the modulator M, oversubstantially the same conduetorsas are utilized in receiving ringingsignals, and at the same time opening both the line and network sides ofthe hybrid coil during the ringing period in such a way that theresistance of the generator does not unbalance the hybrid circuit.

When it is desired to transmit ringing signals to the distant station,the local operator or subscriber impresses a 20 cycle ringing currentupon the low frequency line L, this current be ng impressed over theback contacts of relay 5 upon the alternating current relay 6.

The operation of relay 6 establishes an energizing circuit for relays 7and 8, which may be traced from round, through battery' 9, windings ofre ays 7 and 8 in series, left contact and armature of relay 6 toground. An energizing circuit is likewise established for relay 10,extending from ground, through battery 11, windings of relays 10 and 8in series, left contact and armature of relay 6 to ground. Relay 12 .isalso operated over a circuit extending from ground through battery 13,winding of relay 12, right contact and armature of relay 6 to ground.

The operation of relay 7 disconnects the low frequency line L from theterminals 2 of the hybrid coil H. The operation of relay 10 disconnectstheline balancing network N from the terminals 3 of the hybrid coil. Inactual practice, the functions of relays 7 and 10 have been performedvby a single relay, and it will be understood that separate relays areshown in the drawing merely for the sake of simplifying the showmg.

Relay 12, in operating, opens its right back contacts, thusdisconnecting the receiving ringing apparatus from conductors 14 throughwhich such apparatus is normally connected to terminals 2 of the hybridcoil H in readiness to receive incoming ringing signals. At its. rightfront contacts relay 12 connects the generator G to the conduc tors 14.Relay 12 in opening its left back contact, also opens the circuit ofringing re sponse relay 15 in order to prevent the operation of relay 5during the transmission of ringing signals. This latter precaution istaken to prevent transient capacity effects from actuating the receivingringing circuit when the ,input leads are open during the energizationof relay 12.

Relay 8, when energized over the circuit traced above, disconnects theright conductor 14 from the lower line terminal 2 of hybrid coil H, andconnects this conductor to the lower line terminal 3. Under theseconditions, the 1000-cycle ringing current periodically interrupted at20 cycles is supplied from generator G to the modulator Mover a circuitextending from one pole of generator G through one right front contactand armature of relay 12, conductor 14, upper terminal 2 and linewinding of hybrid coil H, left bridge terminal 4, modulator M, rightbridge terminal 4, line winding and lower terminal 3 of hybrid coil H,front contact and armature of relay 8, conductor 14, right armature andfront contact of relay 12 to the opposite pole of generator G.

The ringing current thus supplied to the modulator M modulates thecarrier current supplied to the modulator from the oscillator TO, andone of the products of modulation, for example, the upper side band, istransmitted by the band filter TBF to the multiplex line ML. The mannerin which the ringing signal is received at the distant terminal will bedescribed in connection with the local terminal circuits shown ,on thedrawing, since the circuits at the local and distant terminals areidentical.

In receivin ringing signals allotted to the channel It the side bandincoming over the line ML will lie within the transmission range of bandfilter RBF. The wave so transmitted by the filter RBF is combined in thedemodulator and amplifier DA with carrier waves from the source R0 toproduce the original ringing frequency of 1000 cycles interrupted at 20cycles. The ringing current in the output circuit of the demodulator andamplifier DA is transmitted through .hybrid coil H and is selectivelytransmitted by tuned circuit 17 to the input circuit of detector 18. The20 cycle com: ponent appearing in the output circuit of detector 18 isimpressed upon polarized relay 19 which is actuated alternately by thepositive and negative impulses.

Upon the operation of relay 19 in the above manner, alternating currentrelay 20 is energized in the manner described in Murphy Patent No.1,537,653, issued May 12, 1925, remaining energized as long as relay 19is operated in response to the incoming signals. Relay 20, in operating,short circuits relay '21 which is normally energized over an obviouscircuit. Relay 21 is of the slow releasing type and is adapted to closeits associated contact only when relay 20 remains energized for apredetermined period, and hence relay 21 will not be deener-' gized ifrelay 20 is momentarily operated in response to voice currents or otherirregular impulses incoming over the line.

Relay 21, inv deenergizing, establishes an operating circuit for relay15 which extendsv through the left armature and contact of relay 12.Hence, if the left contact-of relay 12 is open, as it is during thetransmission of rin ing signalsto the distant terminal as descri edabove, relay 15 can not be enerquency line L and the balancing network Nfrom the hybrid coil H to prevent singing in the carrier circuits. Theoperation of relay 5 also disconnects the low frequency line L from thealternating-current relay 6 to prevent the actuation of this relayduring the reception of signals.

From the above description, it will be seen that by transmitting theringing current diagonally through the hybrid coil, it is unnecessary tosubstitute a net work which simulates the impedance of the 1000 cyclegenerator for the line balancing network during, the signal transmittingoperation.

Since substantially the same conductors 14 are utilized in thetransmission and reception of ringing signals, itwill be .seen that thissystem involves fewer connections between the carrier system and theringing circuits than if the ringing enerator were connected directly tothe bri ge circuit terminals of the hybrid coil.

While only one embodiment of the invention has been shown and described,it will be understood that all embodiments, as defined by the appendedclaims, come within the scope of the invention.

What is claimed is: 1

1. A signaling system comprising a transmission line, outgoing andincoming branch circuits, a plurality of impedance elements connectingsaid line and said branch circuits in conjugate relation, means fordisconnecting said line from said branch circuits, and means controlledby said first mentioned means for transmitting a signal over a pathincluding inseries the outgoing branch circuit and certain of saidimpedance elements.

2. A signaling system comprising a transmission hne, an outgoing branchand an incoming branch, a plurality of impedance elements connecting oneof the branches in bridge of the line and theother branch in serieswith' the line, means for balancing said line to permit independentcommunication between the line and said branches, means fordisconnecting the line from said branches and for simultaneouslyimpressing a signal on said outgoing branch, and means controlled bysaid last mentionedmeans to establish a' path for the outgoin signalinproduce a neutral effect with respect to said incoming branch.

3. A carrier wave signaling system compllSlllg a transmission line, anoutgoing channel and an incoming channel, ahybrid' -coil connecting saidoutgoing channel in bridge of the line and said incoming channel inseries with the line, a line balancing network connected to said hybridcoil, and means for disconnecting said line and balancing network fromsaid hybrid coil and for transmitting a signal over a path including inseries said outgoing channel and a portion of the windings of saidhybrid coil 4. A carrier wave signaling system com prising a lowfrequency line, an outgoing channel andan incoming channel, a hybridcoil connecting said outgoing channel 7 inbridge of the line and saidincoming channel in series with the line, a line balancing networkconnected to said hybrid coil, a

ringing circuit including a pair of conductors normally bridged acrossthe drop side of said chybrid coil to receive incoming ringing signals,switching means for disconnecting said low frequency line and balancingnetwork from said hybrid coil, means controlled by said switching meansfor disconnecting one of the conductors of said ringing circuit from thedrop side of the hybrid coil and connecting it to the network side ofthe hybrid coil, and means for impressing a ringing signal upon saidringing circuit for transmission over a path including in series saidoutgoing channel and a portion of the windings of said hybrid coil.

In witness whereof, I hereunto subscribe my name this 6th day of OctoberA. D.,

' HAROLD M. PRUDEN.

